This invention relates to a cutting cylinder for a document shredding machine and a method for making the cutting cylinder.
In order to destroy documents to preserve their confidentiality, shredders exist which cut the paper into narrow strips or chips. Typically, the cutting is achieved by a pair of cutting cylinders having a series of circular cutters arranged along the axis of a solid shaft. The cutters of one shaft are offset so that the cutters pass between the cutters of the other shaft. In addition, the cutters may be either a straight cut type, which produces narrow strips of paper, or a cross cut type, which produces small paper chips.
Generally, the cutting cylinders used in paper shredders are made in one of two ways. First, the cutters and shaft are machined together to form an integral cutting cylinder of solid metal. The cutting cylinder is then hardened to withstand the rigors of cutting paper. There are several problems, however, with this method of making a cutting cylinder. For instance, extensive machining of a cutting cylinder can be very expensive and is limited in the types and shapes of cutters that can be used for the cutting cylinder. Also, while it is necessary to sufficiently harden the integral cutting cylinder to make it resistant to paper clips and other foreign material, it is both expensive and difficult to do so without the risk of warping the cutting cylinder. Additionally, it is often desirable to use a different material for the cutting shaft than the cutters.
The second way of making a cutting cylinder is to stack individual cutters and spacers onto a shaft with some feature to prevent the cutters from rotating about the shaft, such as a hexagonal cross-section, a groove, or a spline. This method of making a cutting cylinder allows the use of a wide variety of cutting materials and types of cutters, but it requires either expensive stacking machinery or a high labor content. In addition, the use of spacers between the cutters increases the total amount of parts used and the cost of making the shredder. Moreover, in a cross cut type shredder, the indexing of the cutters can result in a level of complexity that makes manual stacking very difficult and costly.
Accordingly, it is an object of the present invention to provide a cutting cylinder for a paper shredder that is an improvement over the above prior art cutting cylinders. In the present invention, a cutting cylinder is provided with a hollow shaft and a plurality of cutter discs arranged along the axis of the shaft. The shaft is expanded outward against and around each of the cutter discs to lock the lateral and rotational positions of the cutter discs about the shaft. As a result, the cutting cylinder of the present invention may have cutter discs with a wide variety of different shapes, cut types, and materials, and yet still have very few parts.
It is also another object of the present invention to provide a method of making this cutting cylinder that is an improvement over the previously described prior art methods of making cutting cylinders for paper shredders. In the method of the present invention, cutter discs are placed in a fixture or mold that correctly spaces them apart and, in the case of cross cut type cutter discs, permits adjustment of their rotational position. A shaft is next slid through the central bores of the cutter discs, and then expanded outward against and around the cutter discs to lock their lateral and rotational positions about the shaft. As a result, the method of the present invention provides a simple, inexpensive, and fast way of making a cutting cylinder for a paper shredder. The method of the present invention also provides a great deal of precision in adjusting the lateral and rotational positions of the cutter discs about the shaft, and permits the use of cutter discs having a wide variety of shapes, cut types, and materials.